Bara bin Azib reported,

My maternal uncle passed by me. Hushaym, in his narration, named him as Harith bin Amr. The Prophet ﷺ had tied a banner for him.I asked him, "Ayn Tureed?"He replied, "The Messenger of Allah ﷺ has sent me to a man who married his father's wife after his father's death, and he ordered me to strike off his neck."

Ibn Majah 2607

Sahih

حدثنا إسمعيل بن موسى حدثنا هشيم ح و حدثنا سهل بن أبي سهل حدثنا حفص بن غياث جميعا عن أشعث عن عدي بن ثابت

عن البراء بن عازب قال

مر بي خالي سماه هشيم في حديثه الحارث بن عمرو وقد عقد له النبي ﷺ لواء فقلت له أين تريد فقال بعثني رسول الله ﷺ إلى رجل تزوج امرأة أبيه من بعده فأمرني أن أضرب عنقه

ابن ماجه 2607صحيح
Contents
Reference
Commentary
Ayat
Collection
Sunan Ibn Majah
Book
Legal punishments
Chapter
Whoever marries his father's wife after him
Numbering
Darussalam 2607
Ibn Majah 2607